-LRB- CNN -RRB- -- Alex Ferguson has defended the Premier League referee at the center of a racism row , saying Chelsea 's allegations are `` unthinkable . ''

Ferguson , one of football 's most venerated and decorated figures , insists he does not believe claims that Mark Clattenburg used `` inappropriate language '' towards Chelsea 's Nigerian midfielder John Obi Mikel during Manchester United 's 3-2 win at Stamford Bridge on Sunday .

While both the police and Football Association have launched an investigation into the alleged incident , Ferguson has stepped in to defend the match official , who has been stood down from duty pending the inquiries .

`` I do n't believe Mark Clattenburg would make any comments like that . I refuse to believe it , '' Ferguson told reporters ahead of United 's game against Arsenal on Saturday .

`` I think it is unthinkable in the modern climate . I just do n't believe it -- simple as that . I 've never had a player come to me in the last 15 years and say a referee swore in a game -- ever .

`` The way we see the game today rather than how it was 25 years ago , it has completely changed .

`` I played myself and I know that the banter which went on between referees and players 25 years ago is different to today .

`` There is no way a referee would stoop to that , I am convinced of that . ''

Police to investigate ` racist ' referee in Chelsea case

Chelsea manager Roberto Di Matteo , whose side takes on Swansea on Saturday , refused to become embroiled in a war of words with Ferguson .

`` It 's a free country and everybody can say what they want , '' the Italian told reporters . `` He likes to talk about other clubs . We tend not to . ''

Police launch hunt for ` racist ' Chelsea fan

Meanwhile , the Chelsea fan who allegedly made racist gestures at United 's Danny Welbeck during Wednesday 's League Cup tie has been named as 28-year-old Gavin Kirkham from the county of Hertfordshire , north of London .

Kirkham was photographed making a `` monkey '' action towards Welbeck , triggering another police investigation .

Chelsea has already vowed to crack down on any acts of racism and Di Matteo insists the London club is determined to eradicate the problem .

`` I always said that we are against any form of discrimination , '' he said .

`` We will support anyone who is fighting that . That 's our position and my personal belief as well .

`` The fact that these incidents are happening give a lot of media exposure and makes people aware that we have to fight maybe a little more strongly than perhaps we thought .

`` Everyone has to be involved in this process to eradicate it from the sport and life in general . ''

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Sir Alex Ferguson backs Mark Clattenburg over allegations of ' `` inappropriate language ''

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Police and FA have launched investigations into allegations

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Roberto Di Matteo refuses to react to Ferguson 's comments

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Chelsea fan who allegedly racially abused Manchester United 's Danny Welbeck named